1. Field of the Invention
The present invention relates to circuit board testing equipment and more specifically to a method and apparatus for testing integrity of electronic circuits.
2. Background Art
Electronic systems rely on circuitry to function properly. Thus, it is desirable to test the circuitry for correctness. Some prior art testing methods require multiple steps to test connectivity and correctness of circuitry. Such testing methods are sometimes inefficient. This problem can be better understood by a review of the circuit testing process.
Advanced Functional Testers
Computer systems are one class of electronic system. A computer system typically utilizes a core circuit board, termed a xe2x80x9cmotherboard,xe2x80x9d to couple all components of the computer system. A computer system operates properly when its motherboard is functioning as designed. Thus, it is desirable to test motherboards for correct functionality before their use.
Testing the motherboard of a computer system is typically achieved using an Advanced Functional Tester (AFT). An AFT tests a computer system motherboard by simulating the load of functionally known components of a computer system (e.g., processor or memory) on the motherboard. Concurrently, an AFT monitors the performance of the motherboard to determine whether it is functioning as designed. However, to insure accurate testing of motherboards, the AFT must be tested for correctness.
FIG. 1 illustrates one embodiment of an AFT. The embodiment is divided into two sections: a base and a fixture. The base section contains the base (100) and one or more connectors termed xe2x80x9cbase connectorsxe2x80x9d (110). These connectors attach to the fixture section (130) through the base connector pins (120). During testing of a motherboard, the base performs the task of conducting the test operations, supplying power to the motherboard and monitoring the motherboard""s performance.
During testing of a motherboard, the fixture simulates the components of the computer system in which the motherboard is designed to operate. Thus, the fixture is fitted with known, working computer components (e.g., processor or memory) (140) used for load simulation, one or more connectors termed xe2x80x9ccomponent connectorsxe2x80x9d (150) used to couple the computer components to the motherboard through network circuits (160) and probes termed xe2x80x9cbed of nails probesxe2x80x9d (170).
During testing, a motherboard receives power from the base after contacting the bed of nails probes. These probes couple the contacted points of the motherboard to the circuit networks, and the circuit networks are coupled to the component connectors. Likewise, the connectors are coupled to the computer components. Thus electrical current and signal information is conducted between the computer components and the motherboard.
It is important that the connections from the bed of nails probes, the circuit networks and the component connectors function as designed for the fixture to correctly simulate load during testing of a motherboard. Thus, the connectivity between the bed of nails probes and the component connectors are tested as part of testing the AFT.
During testing of a motherboard, the base connectors must function as designed for the base to properly perform its tasks of conducting the test operations, supplying power to the motherboard and monitoring the performance of the motherboard. Thus, the base connectors are tested as part of testing the AFT.
FIG. 2 illustrates the steps involved in a prior art method of testing an AFT. At step 200, a shorting board test is performed to test connectivity from the bed of nails probes to the component connectors. At step 210, a connector pin test is performed to test the base connectors. At step 220, a Load Test is performed to test the AFT overall functionality.
Shorting Board Test
A shorting board is a printed circuit board which is entirely conductive on both sides. Consequently, when attached to a connector, the shorting board allows current to flow between all the pins of that connector. Additionally, current flows to all bed of nails probes that are joined to that connector by the circuit networks.
FIG. 3 illustrates a shorting board test sequence of events. At step 300, a shorting board is attached to a component connector. At step 310, current is supplied from the shorting board. At step 320, current flows to the pins of the connector which are attached to the shorting board. At step 330, current flows to the bed of nails probes that contact the component connector pins through the circuit networks. At step 340, an untested bed of nails probe is selected.
At step 350, it is determined whether current reaches the selected probe. If current reaches the probe, at step 360, the circuit has connectivity and the process continues at step 380. If current does not reach the probe, at step 370, the circuit lacks connectivity and the process continues at step 380. At step 380, it is determined whether any untested probes remain. If an untested probe remains, the process repeats at step 340. If all probes are tested, at step 390, shorting board testing is complete.
The shorting board test is performed to determine whether connectivity is present from each bed of nails probe to its respective component connector pin. However, the shorting board test is insufficient in testing that every pin of a connector functions correctly since all connector pins are shorted to each other.
Connector Pin Test
FIG. 4 illustrates one embodiment of a connector pin test. The connector pin test is performed to determine whether each of the base connector pins (420) has continuity to the base. During the test, the base (400) supplies current to the base connectors (410). A DMM (430) is used to detect whether this current reaches each pin of the base connectors. One probe (440) of the DMM is connected to the common (ground) pin (460), and the other probe (450) is connected to the individual pin being tested (470). If the DMM detects a flow of current, the probing pin has continuity to the base. If no flow of current is detected, the probing pin does not have continuity to the base.
Load Test
The load test is performed to ensure the AFT is functioning properly when testing a known working motherboard. FIG. 5 illustrates the load test sequence of events. At step 500, functionally known computer components are attached to the fixture component connectors. At step 510, a motherboard, which is also known to work properly, is attached to the bed of nails probes. At step 520, the motherboard is made to contact the bed of nails probes. At step 530, power is supplied to the motherboard from the base. At step 540, the AFT tests the motherboard. At step 550, it is determined whether the AFT test results show the motherboard works correctly. If the AFT tests results show the motherboard works correctly, at step 560, the AFT functions correctly. If the AFT test results show the motherboard does not work correctly, at step 570, the AFT does not function correctly.
The present invention is a method and apparatus for characterization of electronic circuitry. Electronic systems rely on correct circuitry to function properly. Thus, a testing process is utilized to ensure correctness of circuitry. Some testing methods require multiple steps to test connectivity and correctness of circuitry. These methods are inefficient in some applications. The present invention improves efficiency of the testing process of some electronic systems.
One embodiment of the present invention injects a known current into a circuit at a test point by providing a known voltage across a known resistance. The voltage at the test point is measured and the circuit is characterized by a plot of the known voltage minus the measured voltage with respect to the measured voltage.
One embodiment is used to improve efficiency in testing advanced functional testers. Since a circuit is characterized by the embodiment contacting one test point, continuity and integrity from each connector pin are tested simultaneously. Thus, the need for a shorting board test is eliminated. Other embodiments are used to test other electrical systems.